Light-induced self-writing effects in bulk chalcogenide glass

Abstract

Abstract-A waveguide can be self-written by a beam of light propagating in a photosensitive material. We report the first observation of self-writing effects in bulk chalcogenide glass and investigate the influences of different writing beam sizes and powers. We observe increases in refractive index of 2.5 10 4 due to illumination at 1047 nm in Ce-doped Ga-La-S. Simulations of the self-writing process show a good agreement with the experimental results. This verifies our numerical model and allows the dynamics of this process to be explored. Using this knowledge, we predict the experimental parameters and conditions required to write waveguides, tapers, and ultimately complex three-dimensional (3-D) structures.

Observation of light-induced refractive index reduction in bulk glass and application to the formation of complex waveguides

“…Here two differential equations [1] are used where the paraxial wave equation describes the propagation of light (in the direction z) and the photosensitivity equation describes the change in refractive index (∆n) in response to light (Table 1). Previously a simple model has been shown to agree well with experiments in germanosilicate [2] and chalcogenide glass [3], and in photopolymers [4]. Here we modify this model to describe a decrease in index in response to light.…”

“…Previously, increases in index have been used to self-write channel waveguides in bulk photopolymers [4,5] and in glass in the planar geometry [2]. Recently we showed the first self-writing effects in bulk chalcogenide glass [3]. Self-writing has also been investigated in thin film photopolymers [6] where a decrease in index is induced.…”

“…If the index of the material increases in response to illumination, this area of higher index reduces the diffraction of the incoming beam and over time a self-written channel waveguide can evolve [1,2,3]. These waveguides offer a number of advantages in comparison with other methods of fabricating waveguides such as epitaxial growth, diffusion methods and direct writing.…”

“…In order to also obtain good agreement for the peak intensity, a more complete model for the index change is needed. For example, the effects of absorption need to be included to account for the observed luminescence and induced losses, and in previous work a variable exposure-dependent absorption [3,7] has been shown to improve the agreement.…”

“…Self-writing has also been investigated in thin film photopolymers [6] where a decrease in index is induced. Numerical simulations of self-writing have mainly concentrated on the planar geometry, although it has been shown that channel waveguides can form in a bulk material using a Gaussian writing beam [3,7]. The bulk geometry offers more flexibility to form complex three-dimensional waveguides, however no investigations into writing more complicated structures have been conducted to date.…”